Cloud computing provides a service delivery and consumption mode. A cloud service provider (CSP) uses a network to connect a large number of computing resources and performs unified management, allocation, and scheduling to constitute a huge computing resource pool so as to provide services for cloud service consumers (CSC). Generally speaking, cloud services are roughly classified into three tiers, namely, infrastructure as a service (IaaS, also called tier I), platform as a service (PaaS, also called tier P), and software as a service (SaaS, also called tier S). At present, most cloud service providers in the industry are tier I providers (such as Amazon). In IaaS, a CSC consumes only infrastructure capabilities provided by a CSP, such as computing, storage, and network transmission. Therefore, the CSC must provide a corresponding platform and software application, while the CSP provides tier I services for the CSC by means of a virtual machine.
An application deployed on the CSP generally has architecture with multiple tiers of servers. For example, a Web application deployed on the CSP has a typical three-tier architecture: a Web server tier, an application (App) server tier, and a database (DB) server tier. Servers at each tier may be regarded as one type of servers. Each tier may include multiple servers and each server corresponds to one virtual machine (VM). In the prior art, when the CSP finds by monitoring that a tier is faced up with lots of operations, the CSP increases a quantity of servers at this tier to implement load distribution. Accordingly, servers at other tiers, which are associated with the servers at this tier, will also be faced up with lots of operations. Therefore, quantities of servers at other tiers also need to be increased to implement load distribution. The prior art implements load distribution by adding servers one by one in the servers at the tiers. In the present invention, servers at each tier are one type of servers.
The inventor finds that the foregoing prior art has at least the following disadvantages: Adding servers one by one at different tiers to implement load distribution may cause that, when servers at one tier are faced up with lots of operations, more operations are required on servers at other tiers, which are associated with the servers at this tier, and therefore heavier computing pressure is caused and multiple servers need to be added. Each time a virtual machine corresponding to one server is added, some time is required. Therefore, in a process of adding servers one by one at the tiers, some operation requests on the servers at the tiers may have expired, which causes poor quality of service of an application deployed on the CSP.
For example, when a large number of accesses crowd into the Web application deployed on the CSP, CPU utilization ratio of a Web server will suddenly increase. Because an App server and a DB server are responsible for service logic processing and data addition, deletion, query and modification respectively, computing pressure on the App server and the DB server is much heavier than that on the Web server. Therefore, multiple App servers and DB servers need to be added to process these sudden crowded requests. At present, the CSP adds servers one by one at the App server tier and the DB server tier. Because it takes some time to add servers, in the process of adding servers one by one at the App server tier and the DB server tier, some requests at the Web server tier may have expired, which lowers the quality of service of the Web application on the CSP.